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| United States Patent |
5,634,989
|
|
Hashimoto
, et al.
|
June 3, 1997
|
Amorphous nickel alloy having high corrosion resistance
Abstract
A corrosion-resistant amorphous alloy containing Ta in an amount of from 10
to 40 atomic % and Mo, Cr, W, P, B and/or Si is disclosed.
This alloy can be prepared by rapidly cooling and solidifying molten alloy,
shows a satisfactory corrosion resistance in high-temperature concentrated
phosphoric acid, and is adapted to be used as a plant structural material
or a separator for a fuel cell.
| Inventors:
|
Hashimoto; Koji (Izumi, JP);
Mitsuhashi; Akira (Omiya, JP);
Asami; Katsuhiko (Sendai, JP);
Kawashima; Asahi (Sendai, JP);
Takizawa; Yoshio (Omiya, JP)
|
| Assignee:
|
Mitsubishi Materials Corporation (Tokyo, JP);
Koji Hashimoto (Izumi, JP)
|
| Appl. No.:
|
914027 |
| Filed:
|
July 15, 1992 |
Foreign Application Priority Data
| May 07, 1987[JP] | 62-111465 |
| May 07, 1987[JP] | 62-111466 |
| May 07, 1987[JP] | 62-111467 |
| May 11, 1987[JP] | 62-113939 |
| May 26, 1987[JP] | 62-129286 |
| May 29, 1987[JP] | 62-134367 |
| May 29, 1987[JP] | 62-134368 |
| Current U.S. Class: |
148/403 |
| Intern'l Class: |
C22C 019/05; C22C 027/02 |
| Field of Search: |
148/403,304
|
References Cited
U.S. Patent Documents
| 4133681 | Jan., 1979 | Ray.
| |
| 4410490 | Oct., 1983 | Ray et al.
| |
| 4496635 | Jan., 1985 | Wang et al.
| |
| 4854980 | Aug., 1989 | Raman et al. | 148/403.
|
| 4968363 | Nov., 1990 | Hashimoto et al. | 148/403.
|
| Foreign Patent Documents |
| 0224724 | Jun., 1987 | EP.
| |
| 3608656 | Sep., 1986 | DE.
| |
| 53-57120 | May., 1978 | JP.
| |
| 54-142122 | Nov., 1979 | JP.
| |
| 54-142123 | Nov., 1979 | JP.
| |
| 55-125248 | Sep., 1980 | JP.
| |
| 61-210143 | Sep., 1986 | JP.
| |
| 62-33735 | Feb., 1987 | JP.
| |
| 62-33736 | Feb., 1987 | JP.
| |
| 63-79931 | Apr., 1988 | JP.
| |
| 63-79930 | Apr., 1988 | JP.
| |
Other References
Corrosion Science, vol. 27, No. 9, pp. 957-970, 1987 "The Corrosion
Behavior of Amorphous Nickel Base Alloys in a Hot Concentrated Phosphoric
Acid".
|
Primary Examiner: Simmons; David A.
Assistant Examiner: Phipps; Margery S.
Attorney, Agent or Firm: Cushman, Darby & Cushman IP Group of Pillsbury Madison & Sutro LLP
Parent Case Text
This is a continuation of application Ser. No. 07/339,611, filed on Feb.
24, 1989, which was abandoned.
Claims
What is claimed is:
1. An amorphous nickel alloy having a high corrosion resistance, which
consists of Ta in an amount of from 10 to 40 atomic %, Mo in a total
amount with Ta of from 25 to 50 atomic %, with Mo in an amount of at least
3 atomic %, and the balance Ni.
2. An amorphous nickel alloy having a high corrosion resistance, which
consists of Ta in an amount of from 10 to 40 atomic %, Mo in a total
amount with Ta of from 25 to 50 atomic %, with Mo in an amount of at least
3 atomic %, P in an amount of from 3 to 10 atomic %, and the balance Ni.
3. An amorphous nickel alloy having a high corrosion resistance, which
consists of Ta in an amount of at least 1 atomic %, at least one of Mo and
W in a total amount with Ta of from 15 to 30 atomic %, with Mo in an
amount of at least 3 atomic %, at least one of P, B and Si in an amount of
from 10 to 23 atomic %, and the balance Ni.
4. An amorphous nickel alloy having a high corrosion resistance, which
consist of Mo in an amount of at least 3 atomic %, W in a total amount
with Mo of from 15 to 30 atomic %, at least one of P, B and Si in an
amount of from 10 to 23 atomic %, and the balance Ni.
Description
FIELD OF THE INVENTION
The present invention relates to an amorphous nickel alloy having a high
corrosion resistance, which is suitable as a corrosion-resistant material
in a severe corrosive environment such as high-temperature concentrated
phosphoric acid.
BACKGROUND OF THE INVENTION
As structural materials for a high-temperature concentrated phosphoric acid
plant, 309, 310 and 446 Mo stainless steels and Cr--Mo--Ti steel are
popularly in use at present. Even these materials are not provided with a
corrosion resistance sufficient to withstand a severe corrosive
environment such as high-temperature concentrated phosphoric acid.
The present inventors have previously found amorphous nickel alloys highly
resistant to pit corrosion, interstitial corrosion and uniform corrosion,
and applied for patent under Japanese Patent Provisional Application No.
53-57,120, Japanese Patent Provisional Application No. 61-210,143,
Japanese Patent Provisional Application No. 62-33,735, and Japanese Patent
Provisional Application No. 62-33,736.
Furthermore, the present inventors have continued their studies while
examining various properties of amorphous alloys, and found availability
of an amorphous nickel alloy having a high corrosion resistance through
formation of a stable protecting film even in a severe corrosive acid poor
in oxidizing ability such as hightemperature concentrated phosphoric acid,
on which they have applied for patent under Japanese Patent Applications
Nos. 61-225,435 and 61-225,436.
Japanese Patent Application No. 61-225,435 covers the following four
claims:
(1) An amorphous nickel alloy having a high corrosion resistance, which
comprises Mo in an amount of from 10 to 30 atomic %, P in an amount of
from 15 to 23 atomic %, and the balance essentially Ni.
(2) An amorphous nickel alloy having a high corrosion resistance, which
comprises Mo in an amount of from 10 to 30 atomic %, one or more of B and
Si in an amount of up to 7 atomic % and in a total amount with P of from
15 to 23 atomic %, and the balance essentially Ni.
(3) An amorphous nickel alloy having a high corrosion resistance, which
comprises Mo in an amount of from 10 to 30 atomic %, Cr in an amount of
from 30 to 40 atomic %, P in an amount of from 3 to 20 atomic %, and the
balance essentially Ni.
(4) An amorphous nickel alloy having a high corrosion resistance, which
comprises Mo in an amount of from 10 to 30 atomic %, Cr in an amount of
from 30 to 40 atomic %, one or more of B and Si in an amount of 7 atomic %
and in a total amount with P of from 8 to 20 atomic %, and the balance
essentially Ni.
Japanese Patent Application No. 61-225,436 covers the following seven
claims:
(1) An amorphous nickel alloy having a high corrosion resistance, which
comprises Ta in an amount of from 20 to 60 atomic %, and the balance
essentially Ni.
(2) An amorphous nickel alloy having a high corrosion resistance, which
comprises Ta in an amount of from. 1 to 25 atomic %, P in an amount of
from 15 to 23 atomic %, and the balance essentially Ni.
(3) An amorphous nickel alloy having a high corrosion resistance, which
comprises Ta in an amount of from 1 to 25 atomic %, one or more of B and
Si in an amount of up to 7 atomic % and in a total amount with P of from
15 to 23 atomic %, and the balance essentially Ni.
(4) An amorphous nickel alloy having a high corrosion resistance, which
comprises Cr in an amount of from 10 to 40 atomic %, P in an amount of
from 15 to 23 atomic %, and the balance essentially Ni.
(5) An amorphous nickel alloy having a high corrosion resistance, which
comprises Cr in an amount of from 10 to 40 atomic %, one or more of B and
Si in an amount of up to 7 atomic % and a total amount with P of from 15
to 23 atomic %, and the balance essentially Ni.
(6) An amorphous nickel alloy having a high corrosion resistance, which
comprises Ta in an amount of up to 20 atomic % and in a total amount with
Cr of from 10 to 40 atomic %, P in an amount of from 15 to 23 atomic and
the balance essentially Ni.
(7) An amorphous nickel alloy having a high corrosion resistance, which
comprises Ta in an amount of up to 20 atomic % and a total amount with Cr
of from 10 to 40 atomic %, one or more of B and Si in an amount of up to 7
atomic % and a total amount with P of from 15 to 23 atomic %, and the
balance essentially Ni.
Because of the high boiling point, concentrated phosphoric acid is
particularly corrosive at high temperatures, so that there is available no
metal material which can be safely used. The alloys disclosed in the
above-mentioned Japanese Patent Applications No. 61-225,435 and No.
61-225,436 show a high corrosion resistance even in such an environment.
There is however an increasing demand for development of further various
metal materials capable of withstanding such a corrosive environment where
it is very difficult to use usual metal materials.
DISCLOSURE OF THE INVENTION
An object of the present invention is therefore to provide an alloy capable
of withstanding an environment which hardly passivates a metal, being
non-oxidizing, and exhibits a very severe corrosivity such as
high-temperature concentrated phosphoric acid.
An alloy is usually in the form of crystals in its solid state. However,
when a method of not allowing formation of a long-period regularity to the
atomic arrangement during formation of solid, through, for example,
extra-rapid cooling for solidification from the molten state by limiting
the chemical composition of an alloy, an amorphous structure similar to
liquid is obtained, and the thus obtained alloy is called an amorphous
alloy. In most cases, an amorphous alloy is a uniform singlephase alloy of
a super-saturated solid-solution. It has a far higher strength as compared
with conventional commercial metals, and shows various properties,
depending upon the chemical composition, including an abnormally high
corrosion resistance. The present inventors carried out studies on
utilization of properties of such amorphous alloys, and found as a result
an amorphous nickel-base alloy having a high corrosion resistance not
susceptible to pit corrosion, interstitial corrosion or uniform corrosion
even in very corrosive aqueous solution such as aqueous solution
containing a strong acid or high-concentration chlorine ions, and have
applied for patent under Japanese Patent Provisional Application No.
53-57,120. In addition, the present inventors found another amorphous
alloy having a high corrosion resistance applicable in a severe corrosive
environment such as that containing boiling concentrated nitric acid or
additionally containing an oxidizer, and applied for patent under Japanese
Patent Provisional Application No. 61-21,043. They found another amorphous
alloy having a high corrosion resistance applicable in a severely
corrosive environment such as boiling concentrated chlorine, and applied
for patent under Japanese Patent Provisional Applications Nos. 62-33,735
and 62-33,736. All these are amorphous nickel alloys. Because of the high
boiling point, concentrated phosphoric acid is particularly corrosive at
high temperatures, as described above, and a sufficient corrosion
resistance is not obtained unless the alloy itself has the ability to form
a stable protecting film.
The present inventors carried out further studies while examining the
various properties of amorphous alloys. As a result, they found
availability of new amorphous nickel alloys provided with a high corrosion
resistance through formation of a stable protecting film even in a severe
corrosive acid poor in oxidizing ability such as high-temperature
concentrated phosphoric acid, in addition to the alloys disclosed in the
aforementioned Japanese Patent Provisional Applications Nos. 53-57,120,
61-210,143, 62-33,735, and 62-33,736, and applied for patent under
Japanese Patent Application No. 61-225,435 and Japanese Patent Application
No. 61-225,436.
Moreover, the present inventors further continued their studies on
corrosion resistance of amorphous alloys, and as a result, achieved the
present invention by founding out availability of amorphous nickel alloys
showing a high corrosion resistance even in high-temperature concentrated
phosphoric acid through combination of various elements in addition to the
alloys disclosed in the above-mentioned Japanese Patent Application No.
61-225,435 and Japanese Patent Application No. 61-225,436.
The present invention consists of Claims 1 to 7, the component elements and
their contents of which are shown in Table 1.
TABLE 1
__________________________________________________________________________
Chemical composition (atomic %) of alloys of the present invention
Claim
No. Ta Mo Cr Mo. Cr
Mo. W
P Ni(*1)
__________________________________________________________________________
1 10-40 25-50(*2) Balance
2 at least 10,
25-50(*2) Balance
up to 25
3 10-40 25-50(*3) Balance
4 10-40 25-50(*2) Under 10
Balance
5 10-40 25-50(*3) Under 10
Balance
6 at least 1 15-30(*4)
10-23(*6)
Balance
7 15-30(*5)
10-23(*6)
Balance
__________________________________________________________________________
(*1) Essentially Ni
(*2) Total amount with Ta
(*3) Total amount of Mo, Cr and Ta
(*4) Total amount of at least one of Mo and W, with Ta
(*5) Total amount of Mo in an amount of at least 3 atomic % with W
(*6) Total amount of one or more of B and Si, with P, provided that the
total amount of one or more of B and Si is up to 7 atomic %.
The amorphous alloys available by various methods for preparing amorphous
alloys through extra-rapid cooling and solidification of molten alloys of
the above-mentioned chemical compositions or sputter deposition thereof
are single-phase alloys in which the above elements are uniformly
dissolved. A very uniform protecting film which ensures a high corrosion
resistance is therefore produced on any of the amorphous nickel alloys of
the present invention.
A metal material easily melts in high-temperature concentrated phosphoric
acid solution poor in oxidizing ability. In order to use a metal material
in such an environment, therefore, it is necessary to impart the ability
to produce a stable protecting film to the metal material. This is
accomplished by preparing an alloy containing effective elements in
required amounts. In the case of a crystalline metal, however, addition of
diverse alloy elements in large quantities often results in a
multiple-phase structure comprising different chemical properties, and a
desired corrosion resistance cannot be achieved. Generation of chemical
non-uniformity is detrimental to corrosion resistance.
In contrast, the amorphous alloy of the present invention is a uniform
solid-solution and uniformly contains effective elements in required
amounts capable of forming a stable protecting film. A uniform protecting
film is produced and gives a sufficiently high corrosion resistance in
such an amorphous nickel alloy,
More particularly, the condition to be satisfied by a metal material to
withstand high-temperature concentrated phosphoric acid poor in oxidizing
power is to have a high ability to form a stable protecting film to be
uniformly produced on the material in a non-oxidizing environment. This is
achieved by means of the chemical compositions of the alloys of the
present invention, and the fact that an alloy has an amorphous structure
permits preparation of an alloy with a complicated chemical composition
into a single-phase solid-solution and ensures formation of a uniform
protecting film.
Now, the reasons of limiting the chemical composition in the present
invention are described below.
Ni is an element forming the basis of the alloys of the present invention,
which forms an amorphous structure in the presence of at least one of Mo
and Cr in a prescribed total amount with Ta, and forms an amorphous
structure also in the presence of P. Ni assists the effects of Ta, Mo, Cr
and W responsible for corrosion resistance.
Ta, Mo, Cr and W are elements responsible for corrosion resistance through
formation of a protecting film. When the total content of Ta and any of
the other elements is from 25 to 50 atomic %, a metal-metal alloy thereof
with Ni can form an amorphous structure. The total content of at least one
of Mo and Cr with Ta is therefore specified to be from 25 to 50 atomic %
in Claims 1 to 5 of the present invention. However, to avoid duplication
with the alloy disclosed in the above-mentioned Japanese Patent
Provisional Application No. 62-33,735 in the case of an alloy not
containing Mo, the total content of Cr with Ta in an alloy containing Ta
in an amount of at least 25 atomic % should be under 30 atomic %. P is an
effective element which assists formation of a protecting film of Ta, Mo,
Cr or W. However, because addition of P in a large amount to a metal-metal
alloy makes it difficult to obtain an amorphous structure, the P content
is set forth to be under 10 atomic % in Claims 4 and 5 of the present
invention.
In an Ni-P alloy, on the other hand, a high content of P produces an
amorphous structure as a metal-semimetal alloy. However, addition of
excessive p rather hinders formation of an amorphous structure. For the
purpose of producing an amorphous structure, therefore, the P content is
limited within the range of from 10 to 23 atomic % in Claims 6 and 7 of
the present invention. As an amorphous metal-semimetal alloy containing P
in a sufficient amount as above has a high ability to form a protecting
film, the alloy of Claim 6 of the present invention can have a sufficient
corrosion resistance even in severely corrosive high-temperature
concentrated phosphoric acid, if the total amount of at least one of Mo
and W with Ta in an amount of at least 1 atomc % is at least 10 atomic %.
Similarly, an amorphous metal-metal alloy can have a sufficient corrosion
resistance in severely corrosive high-temperature concentrated phosphoric
acid, if the total amount of W in an amount of at least 3 atomic % and W
is at least 10 atomic %, as in that claimed in Claim 7 of the present
invention. In the case of a metal-semimetal alloy, addition of excessive
Mo, W or Ta makes it difficult to obtain an amorphous structure. The total
amount of at least one of Mo and W with Ta in an amount of 1 atomic % is
therefore specified to be up to 30 atomic in Claim 6 of the present
invention, and the sum of Mo in an amount of at least 3 atomic % and W is
set out to be up to 30 atomic % in Claim 7 of the present invention.
B and Si are elements effective for the formation of an amorphous structure
in the presence of Ni and can replace P. However, in order not to reduce
the effect of P of promoting formation of a protecting film, it is not
desirable that P should be replaced by one or more of B and Si in a total
amount of over 7 atomic %.
The amorphous nickel alloy of the present invention may contain Nb in an
amount of up to 10 atomic %, and Ti and Zr in an amount of up to 5 atomic
% without impairing the object of the present invention.
For the preparation of the amorphous alloy of the present invention, any of
the various popularly utilized methods for preparing an amorphous alloy
may be applied, including that of extra-rapidly cooling and solidifying
liquid alloy, those of forming an amorphous alloy through the gaseous
phase, and that of destroying the long-period structure of solid through
ion injection.
An apparatus for preparing the amorphous alloy of the present invention is
illustrated in FIG. 1. In FIG. 1, the portion enclosed by the dotted line
is evacuated into vacuum, and then filled with inert gas. In this figure,
2 is a silica tube having a vertical nozzle 3 at the lower tip thereof,
and the raw material 4 and the inert gas for preventing oxidation of the
raw material 4 can be introduced through an inlet port 1 provided on the
top of the silica tube 2. A heating furnace 5 is installed around the
silica tube 2 to heat the above-mentioned raw material 4. A high-speed
rotating roll 7 is placed vertically below the nozzle 3, and is rotated by
means of a motor 6. When preparing an amorphous alloy, the raw material 4
having a prescribed chemical composition is charged in the silica tube 2,
and first evacuating the apparatus to a vacuum of about 10.sup.-5 Torr,
the tube is filled with inert gas.
Then, the raw material 4 is heated and melted in the heating furnace 5, and
the resulting molten metal is ejected by means of compressed inert gas
onto the outer peripheral surface of the roll 7 rotating at such a high
speed as from 1,000 to 10,000 rpm by the action of the motor 6.
Application of this method permits preparation of the amorphous alloy of
the present invention as a long sheet having, for example, a thickness of
0.1 mm, a width of 10 mm, and a length of several meters.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic view illustrating an apparatus for the preparation of
the amorphous alloy of the present invention. In FIG. 1, 1: raw material
inlet port, 2: silica tube, 3: nozzle section, 4: raw material, 5: heating
furnace, 6: motor, and 7: high-speed rotating roll.
EXAMPLE
Raw material metals were mixed so as to give the chemical compositions
shown in Table 2, and raw material alloys were prepared in an argon arc
melting furnace. These alloys were remelted in argon atmosphere, and
extra-rapidly cooled and solidified by the application of the single roll
method as shown in FIG. 1 into amorphous alloy sheets having a thickness
of from 0.01 to 0.05 mm, a width of from 1 to 3 mm and a length of from 3
to 20 m. Formation of an amorphous structure was confirmed by means of
X-ray diffraction. The surfaces of these alloy specimens were ground in
cyclohexane up to silicon carbide paper No. 1000. Then alloy specimens of
a prescribed length were cut, immersed in about 63% P.sub.2 O.sub.5
solution at 160.degree. C. and 72% P.sub.2 O.sub.5 solution at 200.degree.
C. for a period of from 7 to 10 days, and the weight before and after
immersion was measured by means of a micro-balance. The results obtained
are shown in Table 3.
TABLE 2
______________________________________
Chemical composition of alloys (atomic %)
Claim Specimen
No. No. Ni Ta Mo Cr W P
______________________________________
1 1 70 10 20
2 75 20 5
3 70 20 10
4 60 20 20
5 60 30 10
6 60 30 20
2 7 60 10 30
8 60 20 20
9 61 24 15
10 56 24 20
3 11 65 10 20 5
12 55 20 15 10
13 60 30 5 5
4 14 63 10 20 7
15 62 20 10 8
16 43 30 15 7
17 49 40 5 6
5 18 56 10 15 10 9
19 57 20 10 10 3
20 60 25 5 5 5
6 21 67 1 14 13
22 65 1 15 19
23 63 3 15 19
24 61 5 15 19
25 60 20 10 10
26 63 3 15 19
27 64 20 5 11
28 63 3 10 5 19
29 61 5 15 14 14(B:5)
30 61 5 15 15 15(Si:4)
31 61 5 15 15
##STR1##
32 64 8 16 16
##STR2##
33 62 3 16 1
##STR3##
7 34 63 3 15 19
35 66 5 10 19
36 66 10 5 19
37 56 15 10 24
38 61 17 3 14(B:5)
39 63 15 3 16(Si:3)
40 62 15 3
##STR4##
______________________________________
TABLE 3
______________________________________
Examples of corroding rate (g/hm.sup.2) of the alloys of the
present invention in phosphoric acid solution
Specimen
No. 63% P.sub.2 O.sub.5, 160.degree. C.
72% P.sub.2 O.sub.5, 200.degree. C.
______________________________________
1 0.0622 0.225
2 0.0331 0.154
3 0.0222 0.094
4 0.0132 0.146
5 0.0127 0.045
6 0.0133 0.046
7 0.0635 0.365
8 0.0531 0.122
9 0.0201 0.090
10 0.0192 0.085
11 0.0597 0.213
12 0.0195 0.136
13 0.0125 0.045
14 0.0355 0.185
15 0.0177 0.134
16 0.0098 0.035
17 0.0075 0.021
18 0.0347 0.201
19 0.0163 0.127
20 0.0099 0.035
21 0.0345 0.210
22 0.0303 0.195
23 0.0213 0.187
24 0.0197 0.173
25 0.0233 0.171
26 0.0670 0.251
27 0.0252 0.183
28 0.0233 0.195
29 0.0211 0.196
30 0.0208 0.196
31 0.0214 0.187
32 0.0625 0.244
33 0.0230 0.188
34 0.0435 0.353
35 0.0403 0.282
36 0.0391 0.237
37 0.0353 0.218
38 0.0410 0.266
39 0.0407 0.281
40 0.0413 0.277
______________________________________
The corroding rate of the amorphous alloys of the present invention is very
slight. As a result of analysis of the alloy surface by the application of
the X-ray photoelectron spectrometry after the immersion test of the alloy
of the present invention, a protecting film of hydrated oxide of
concentrated Ta and Mo or hydrated oxyhydroxide was produced on the alloy,
and this was found to be the cause of the high corrosion resistance of the
alloy of the present invention.
INDUSTRIAL USE
The amorphous nickel alloy of the present invention is, as described above
in detail, highly corrosion-resistant in that it is not corroded through
formation of a stable protecting film even in a severely corrosive
environment poor in oxidizing ability such as high-temperature phosphoric
acid.
Since any of the popularly applied known techniques for the preparation of
an amorphous alloy is applicable to the preparation of the alloy of the
present invention, it is not necessary to use a special apparatus, thus
providing excellent practical utility of the alloy of the present
invention.
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